In diagnosing and treating certain medical conditions, it is often desirable to perform a biopsy, in which a specimen or sample of the suspicious tissue is removed for pathological examination, tests and analysis. As is known, obtaining a tissue sample by biopsy and the subsequent examination are typically employed in the diagnosis of cancers and other malignant tumors, or to confirm that a suspected lesion or tumor is not malignant. The information obtained from these diagnostic tests and/or examinations is frequently used to devise a therapeutic plan for the appropriate surgical procedure or other course of treatment.
In many instances, the suspicious tissue to be sampled is located in a subcutaneous site, such as inside a human breast. Such removal of tissue samples may be accomplished by open surgical technique, or through the use of a specialized biopsy instrument and techniques. To minimize surgical intrusion into patient""s body, it is often desirable to insert a small instrument, such as a biopsy needle, into the body for extracting the biopsy specimen while imaging the procedure using fluoroscopy, ultrasonic imaging, x-rays, MRI or any other suitable form of imaging technique. Examination of tissue samples taken by biopsy is of particular significance in the diagnosis and treatment of breast cancer. In the ensuing discussion, the biopsy and treatment site described will generally be the human breast, although the invention is suitable for marking biopsy sites in other parts of the human and other mammalian body as well.
Periodic physical examination of the breasts and mammography are important for early detection of potentially cancerous lesions. In mammography, the breast is compressed between two plates while specialized x-ray images are taken. If an abnormal mass in the breast is found by physical examination or mammography, ultrasound may be used to determine whether the mass is a solid tumor or a fluid-filled cyst. Solid masses are usually subjected to some type of tissue biopsy to determine if the mass is cancerous.
If a solid mass or lesion is large enough to be palpable, a tissue specimen can be removed from the mass by a variety of techniques, including but not limited to open surgical biopsy, a technique known as Fine Needle Aspiration Biopsy (FNAB) and instruments characterized as xe2x80x9cvacuum assisted large core biopsy devicesxe2x80x9d.
If a solid mass of the breast is small and non palpable (e.g., the type typically discovered through mammography), a relatively new biopsy procedure known as stereotactic needle biopsy may be used. In performing a stereotactic needle biopsy of a breast, the patient lies on a special biopsy table with her breast compressed between the plates of a mammography apparatus and two separate x-rays or digital video views are taken from two different points of view. A computer calculates the exact position of the lesion as well as depth of the lesion within the breast. Thereafter, a mechanical stereotactic apparatus is programmed with the coordinates and depth information calculated by the computer, and such apparatus is used to precisely advance the biopsy needle into the small lesion. Depending on the type of biopsy needle(s) used, this stereotactic technique may be used to obtain cytologic specimens, e.g., obtained through FNAB or it may be used to obtain histologic specimens e.g., obtained through coring needle biopsy. Usually at least five separate biopsy specimens are obtained from locations around the small lesion as well as one from the center of the lesion.
The available treatment options for cancerous lesions of the breast include various degrees of mastectomy or lumpectomy and radiation therapy, as well as chemotherapy and combinations of these treatments. However, radiographically visible tissue features, originally observed in a mammogram, may be removed, altered or obscured by the biopsy procedure. In order for the surgeon or radiation oncologist to direct surgical or radiation treatment to the precise location of the breast lesion several days or weeks after the biopsy procedure was performed, it is desirable that a biopsy site marker be placed in or on the patient""s body to serve as a landmark for subsequent location of the lesion site. While current radiographic type markers may persist at the biopsy site, an additional mammography generally must be performed at the time of follow up treatment or surgery in order to locate the site of the previous surgery or biopsy. In addition, once the site of the previous procedure is located using mammography, the site must usually be marked with a location wire which has a barb on the end which is advanced into site of the previous procedure. The barb is meant to fix the tip of the location wire with respect to the site of the previous procedure so that the patient can then be removed from the confinement of the mammography apparatus and the follow-up procedure performed. However, as the patient is removed from the mammography apparatus, or otherwise transported the position of the location wire can change or shift in relation to the site of the previous procedure. This, in turn, can result in follow-up treatments being misdirected to an undesired portion of the patient""s tissue.
As an alternative or adjunct to radiographic imaging, ultrasonic imaging and visualization techniques (herein abbreviated as xe2x80x9cUSIxe2x80x9d) can be used to image the tissue of interest at the site of interest during a surgical or biopsy procedure or follow-up procedure. USI is capable of providing precise location and imaging of suspicious tissue, surrounding tissue and biopsy instruments within the patient""s. body during a procedure. Such imaging facilitates accurate and controllable removal or sampling of the suspicious tissue so as to minimize trauma to surrounding healthy tissue.
For example, during a breast biopsy procedure, the biopsy device is often imaged with USI while the device is being inserted into the patient""s breast and activated to remove a sample of suspicious breast tissue. As USI is often used to image tissue during follow-up treatment, it may be desirable to have a marker, similar to the radiographic markers discussed above, which can be placed in a patient""s body at the site of a surgical procedure and which are visible using USI. Such a marker enables a follow-up procedure to be performed without the need for traditional radiographic mammography imaging which, as discussed above, can be subject to inaccuracies as a result of shifting of the location wire as well as being tedious and uncomfortable for the patient.
The invention is directed generally to devices and methods of marking a biopsy site, so that the location of the biopsy cavity is readily visible by ultrasonic imaging, as well as by conventional imaging methods, such as x-rays. The biopsy site marker of the invention is a persistent marker which may be identified and located by ultrasound visualization.
The biopsy site markers of the invention have a body conformation to enhance acoustical reflective signature or signal. The body conformation may include boundaries of high contrast of acoustic impedance to enhance ultrasound reflection. The markers are readily detected by USI and present a substantial acoustic signature from a marker with small physical dimensions or size. Because of the high acoustic reflectivity of the markers of the invention, the marker size may be reduced to dimensions determined by the physical limits of the imaging system itself, e.g., the ultrasound (US) beam width, without requiring a larger or excessive marker size to reflect sufficient US energy to be noticeable.
In one embodiment, the biopsy site markers of the invention have a characteristic body shape which is recognizably artificial during medical imaging, so as to be readily distinguishable from biological features within the marked tissue. In particular, the markers are readily distinguishable in the various imaging procedures from diagnostically important tissue features, such as lines of calcifications which frequently are signs for a developing malignancy. The marker body shape may have one or more distinct features which may be visualized in different marker orientations. The shape may correspond to a generally known symbol, so a to enhance recognition.
In another embodiment, the markers of the invention have a body conformation to enhance the acoustic signature or signal, so that the body has high acoustic reflectivity when situated in tissue. The acoustic reflective signature of the markers depends on a number of factors. The marker may comprise a composition which presents at least one boundary of high contrast in acoustic impedance to incident US energy, effectively reflecting the US energy to be received by the imaging system. Acoustic impedance (Al) of a material is equal to the product of the characteristic density (xcfx81) of the material and the acoustic velocity (c) in the material, (i.e., Al=xcfx81xc3x97c). As an incident US beam encounters a boundary with a large change in acoustic impedance (e.g., at the marker surface or internal to the marker), much of the US energy is effectively reflected.
Different types of tissue have a wide range of acoustical impedance, for example lung tissue with high air content having low acoustical impedance as compared to bone tissue having high mineral content. However, for uses such as biopsy site marking in typical mammalian soft tissue of high aqueous content, the typical range of tissue acoustical impedance is intermediate these extremes. The composition and body conformation of the markers of the invention may be selected so as to provide boundaries of high contrast of acoustic impedance with respect to the particular tissue site of use.
In an embodiment of the invention, the marker may have a composition in which a base or matrix substance of the marker body (e.g., stainless steel) has an acoustic impedance substantially higher than the tissue at the marked body site. For example, typical bio-compatible metal materials, such as stainless steel, titanium, platinum and the like, generally have acoustic impedance values in the range of 15 to more than 30 times that of typical soft tissue of high aqueous or fatty content. The high acoustic impedance of the marker body base material relative to the surrounding tissue presents a reflective interface to an incident US beam.
A suitable marker body composition with acoustic impedance substantially higher than the tissue at the marked body site is 316L stainless steel. Other alternative compositions, such as compositions of bio-compatible metals, ceramics, metal oxides or polymers, or composites or mixtures of these materials, may be suitable. The marker body may also be radio-opaque.
In another embodiment of the invention, the marker may have a composition in which marker body includes one or more (preferably a large plurality) of internal bounded spaces, such as voids, pores, discontinuities, inclusions, bubbles and the like. These internal spaces preferably contain or entrain air or other gases.
Air has an extremely low acoustic impedance relative to the marker body base or matrix substance. This is true even for matrix materials which themselves have acoustic impedance close to that of the surrounding tissue (e.g., some bio-compatible polymers). The marker body presents internal boundaries of high contrast in acoustic impedance, i.e., at the boundary between the matrix and each internal air-filled space. The marker body thus presents plurality of reflective interfaces to an incident US beam.
Alternatively or in combination with to the materials of high acoustic impedance described above, a marker body with internal voids or air spaces may, if desired, comprise a matrix or base composition which has an acoustic impedance close to that of the tissue at the marked body site, since the air or other gas within the internal spaces provides a dramatic contrast to the matrix material. Suitable bio-compatible materials include polyethylene, polytetrafluoroethylene, PEBAX (made by Autochem Corp.), and the like.
The body matrix material can have a hydrophobic composition or be treated to be hydrophobic. The surface area bounding internal open-cell pores should be hydrophobic so as to resist the displacement of air or other gases in the pores by aqueous fluid from the surrounding tissue, particularly in the case of relatively large pore or space size.
In some embodiments of the invention, the markers can include surface characteristics which enhance the acoustic signature and improve visibility under US imaging, as opposed to a smooth, rounded body surface. In order to provide enhanced ultrasound imaging visibility from all directions of US impingement, the biopsy marker can have a plurality of reflective external surfaces. By making the surface of an object lobulate, multifaceted or otherwise irregular, more reflective surfaces are created, and a brighter acoustic signature is achieved.
For example, a smooth solid sphere provides at least some reflective surface oriented in each direction, but the reflection is achieved over a small portion to the area of the sphere, thus producing an unremarkable acoustic signature. In contrast, an object of the same composition and average diameter as the sphere, but with a highly irregular surface texture, a much brighter acoustic signature or signal is achieved. Thus, the by providing more reflective surfaces of differing or random orientation, the markers appears brighter in US imaging.
The signal-enhancing body conformation may include non-smooth surface texture, such as a porous, frosted, matte, pitted, peened, or scratched surface texture, and the like. The body conformation may also include a multi-element surface contour, such as a faceted, multi-planar, lobulate, coiled, grooved, folded, or inlet surface contour, and the like. Such external body conformations may be used in combination with one another and in combination with the internal discontinuities or air spaces described above.
The body length, diameter or other characteristic scale dimensions of some embodiments of the biopsy marker of the invention may be of a range of sizes. The optimum dimensions of the body will depend upon the specific selected factors which influence acoustic signature as described herein, such as material impedance, surface contours, surface texture, and internal conformation. In addition, the optimum size may depend upon such factors as the type of ultrasound imaging/visualization system used, its imaging resolution, the operating ultrasound frequency, and the biophysical nature of the tissue of interest.
The body dimensions may be selected so as to be large enough to provide a distinct, recognizable marker image within the tissue biopsy site, when visualized under the particular imaging system and operating conditions of use. The body dimensions may also be selected to be small enough to avoid masking or obscuring diagnostically important tissue features. Thus different marker dimensions may be selected to suit particular biopsy site tissue types, and to suit particular known and future medical imaging equipment.
In terms of over-all size, it is desirable that the marker have at least one dimension which is about as large as or greater than the beam width of the USI system with which it is to be visualized. Typically, for current USI systems, the marker will have at least one dimension of about 1 mm or greater, and preferably of at least about 1.5 mm.
In addition, for convenience in applying the marker to the tissue site, the specific marker dimensions and shape may be selected so as to accommodate the dimensions of a particular known or novel biopsy needle device or sampling apparatus, while still achieving a distinct and recognizable marker image under medical imaging as placed at the tissue site. By selecting a marker size and shape to fit within the internal diameter of a biopsy needle or sampling device, the marker may be implanted or applied to the biopsy cavity during the course of the biopsy procedure, following sample recovery but prior to removal of the biopsy device. For example, the marker of the invention may have a size and shape selected to permit application of the marker through the hollow interior space of a vacuum assisted large core biopsy device, such as is commercially available from Johnson and Johnson, Ethicon Endosurgery Division. The small physical size of the markers of the invention relative to their acoustic reflectivity permits fitting the markers to a wide variety of biopsy devices.
In terms of the size of features, including external or internal pores, texture features, facets and the like, it is preferable that these features have a characteristic dimension approximately equal to or exceeding the wavelength of the US beam of the imaging system. For example, with current imaging systems, for a marker with internal air-filled pores, the pore size is typically from about 1 micrometer to 100 micrometers and preferably from about 5 micrometers to 40 micrometers, to provide high reflectivity of the incident US energy.
Optionally, some embodiments of the biopsy site marker of the invention may have elements which assist in accurately fixing the marker to the biopsy site so as to resist migration from the biopsy cavity. Such migration can occur when a placement instrument is withdrawn, and when the marked tissue is subsequently moved or manipulated, as for example when a breast is decompressed and removed from the mammography apparatus. In one embodiment, one or more tissue engaging structures or haptic elements are mounted or affixed to the main marker body, so as to resist movement or migration of the marker from the biopsy site in which it has been implanted during use.
In another embodiment, the biopsy site marker may comprise a pellet-shaped element which encapsulates the high impedance marker body, and assists in resisting migration. The encapsulating pellet may be of a composition, such as gelatin, which is absorbed or dissipated over time, leaving the persistent marker body at the tissue site. In yet another embodiment, the marker body (and/or the optional encapsulating element) may include an adhesive component to cause the marker body (or encapsulating element) to adhere to adjacent tissue within the biopsy site.
A method of the invention for marking a tissue site of interest can include implanting one or more of the markers of the invention, such as one of the exemplary marker embodiments described herein, in or adjacent to a tissue site of interest, e.g., within a biopsy cavity. The marker may then be visualized in situ, such as for purposes of subsequent medical and surgical procedures. The visualization may be by various known medical imaging systems and methods, and in particular may be visualized by known USI systems.
Biopsy markers of the invention can be deposited in accordance with the various methods and techniques utilized in the state of the art. One technique of applying the biopsy markers of the invention is to place or deposit them in a biopsy cavity that is created with a vacuum assisted large core biopsy device. An applicator particularly suitable for insertion of the biopsy site markers of the invention is described below. However, it should be understood that the biopsy markers of the invention can be used without the exemplary applicator device described herein. The biopsy marker applicator disclosed in co-pending application Ser. No. 09/343,975 filed Jun. 30, 1999, may be used to apply the markers of the current invention to a biopsy site. The dimensional size of the applicator device (particularly the inside diameter) may be adjusted to correspond to a selected diameter or characteristic dimension of the biopsy site marker embodiment of the present invention.